Charles Darwin, a naturalist formulated the concept of Natural Selection.
In the year 1859, he published the book “Origin of Species” which included this concept and explained its relationship with evolution.
Natural selection is the mechanism of evolution and it is the natural way of selecting the best and most adapted individuals of a species.
Variation is responsible for generation of new characters in the environment. It occurs due to mutations or changes in genetic compositions over time.
Newer and better adapted characteristics are favoured by nature and organisms that have adaptable features survive and reproduce. This is also known as survival of the fittest.
As these organisms can better reproduce in a particular environment, they give rise to new progenies in large numbers having similar features.
In this way natural selection prefers one organism over another and helps in evolution.
Natural selection also facilitates speciation i.e. generation of new species from older ones. As a result, new species with different and better characters are formed.
Modern Synthetic Theory is based of variations in alleles occurring in a population. Factors are as follows −
Mutations are minute changes occurring in the DNA of an organism which leads to different phenotypes and alters the ability of an organism to adapt in an environment. Mutations can occur during DNA replication, transcription, cell division, etc. It can either be point mutations or frameshift mutations. Some mutations are deleterious while some can be advantageous leading to evolution.
The transfer of DNA from parent to offspring is known as hereditary. It helps the future generations as good changes or good characteristics get transferred from one generation to another. In this process the adaptive characters required for evolution are transferred from the parents to the offspring. This is the mechanism by which a particular adaptive feature multiplies in the population.
It is a classic mechanism to incorporate variation in organisms. Recombination is the combination of new characters from already available ones. It is a process that occurs during meiosis, where the chromosomes undergo crossing over and exchange genetic material between non-sister chromatids. As a result, new genes are shifted to the daughter cells and hence bring about variation in a species. This mechanism is the reason why parents and offspring are not totally identical to each other.
Natural selection literally means selected by nature. Here, nature prefers few traits as compared to others. Hence, individuals with these traits are selected by the environment and are able to survive and reproduce. It assists in variation and evolution by allowing only favorable characters to move ahead and removes the weak or unfavorable traits from the population.
It is the main mechanism of speciation. Isolation causes the separation of two individuals of a species and prevents them from reproducing. This helps in maintaining the originality of a particular species. It is also responsible for evolution because, as individuals are isolated they have to adapt and change as per new conditions, and hence new characteristics are evolved which help to survive.
Evolution is not because of natural selection or genetic composition singularly, but it is a combined effect of both of these mechanisms.
Allele frequency is the no. of different/varied alleles present in a population.
One of these alleles is selected through natural selection and becomes part of the genetic composition of an individual and that is allowed to multiply.
Hence, changes in allele frequency due to variations lead to evolution.
Ecological isolation - When two species are capable of interbreeding, but are isolated as their habitats are in different locations, then such isolation is known as ecological or habitat isolations. E.g. Lion and Tiger can interbreed but do not reproduce since one lives in grasslands and other lives in forests.
Behavioural isolation - When two organisms capable of interbreeding but do not have same behavioural patterns during the mating season, which prevents reproduction, then such an isolation is known as behavioral isolation. E.g. Some birds during mating produce different songs, some dance and some are attracted to particular scents.
Geographical isolation - When organisms capable of interbreeding are isolated due geographical barriers (rivers, mountains, valleys, etc.) then such an isolation is Geographical isolation. E.g. One male lion is on an island and another female lion is on the mainland, they cannot surpass the distance between them and hence are isolated from each other.
Mechanical or Chemical isolation - When reproductive structures are not compatible with one another it does not allow easy transfer of gametes, also there are various chemicals released by organisms that do allow inbreeding such isolation is known as mechanical or chemical isolation. E.g. shape of the flower is not compatible with the natural pollinator.
Temporal isolation - When two organisms which are capable of interbreeding, but cannot reproduce as individuals do not mature at the same time, then such an isolation is known as Temporal isolation. E.g. organisms maturing in different seasons such as spring, autumn, winter etc.
The modern synthetic theory also known as Neo-darwinsm is a mixture of two concepts- Natural Selection and Mendelian genetics. It states that - Changes in allele frequency in a population are the basis of Evolution. It occurs due to variations seen in the germ cells which are passed from one generation to another. Important factors include Mutation and Recombination in DNA. Isolations are also responsible for evolution as it impels organisms to adapt to the changing environment and reproduce in those conditions.
Q1. What is speciation?
Ans. The process of formation of new species from the existing ones is known as speciation. It occurs when individuals of a particular species get separated from its own members and develop unique features. E.g. Galapagos finches.
Q2. Explain survival of the fittest concept?
Ans. This concept was given by Charles Darwin in the theory of natural selection. It states that only those organisms that will survive in the changing environment which can fit and reproduce. It focuses more on reproductive fitness which says that species that reproduce the maximum will survive for a longer duration. Those individuals who are not strong enough will perish.
Q3. Explain Allopatric and Sympatric speciation?
Ans. Allopatric speciation- When a particular species is divided into two groups due to some geographical barriers such as a mountain or river etc., which prevents reproduction amongst them, then they are known as Allopatric speciation. Here the isolated groups now form unique features pertaining to the new environment.
Sympatric speciation- In this type of speciation the organisms live in the same habitat initially they can interbreed but as time lapses they evolve with different characters and cannot breed with the old species. This leads to the formation of new species.
Q4. What is Evolution?
Ans. The gradual process of changes in characteristics of species which helps in adapting to the ever changing environment is known as evolution. It is based on natural selection of traits and brings diversity amongst various organisms.
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